There are several reasons why patients may “reject,” or “spit” sutures. Most commonly, if sutures are placed too superficially and are a large caliber suture, then the knot may be palpable (i.e. you can feel it with your finger) below the skin. Over time, the knots from these sutures can cause friction on the immature overlying scar tissue and gradually work their way through. This can occur with both absorbable sutures (i.e. Monocryl, Vicryl, & PDS) as well as with non-absorbable sutures (i.e Nylon, Silk, & Prolene).
Absorbable sutures absorb through your own body’s inflammatory reaction to the suture material. Occasionally, that process can become colonized with bacteria and the suture knot can become infected. This is called a suture abscess. The treatment for this problem is simply to remove the suture.
Non-absorbale monofilament sutures (i.e Nylon, Prolene) are just that: they are non-absorbable. Most of them are made out of inert material and do not cause much reaction from the surrounding tissues. Non-absorbable sutures are safe to be buried below the skin, as long as they are buried deep within the tissues. When they are placed too close (superficial) to the skin, they can erode through to the surface. Braided non-absorbable sutures (i.e Ethibond, Silk or Mersilene), although softer than non-braided sutures, can also become problematic. Even though braided sutures work very well, because they are braided they tend to harbor bacteria much more easily in the cracks and crevices of the braids. Therefore, should they become exposed to bacteria in your body, they need to be removed.